Two speed drives are known well in the art and have been used successfully for many years. The prior art designs of two speed drives experienced problems with the braking and clutching systems, the planetary gearing arrangements as well as the overall lubrication of the components of the press drive. These prior art designs of two speed drives utilized a plurality of dry clutch plates to hold and/or release the various members of the planetary system. Due to the wear between these friction plates, the drives required constant adjustment and replacement of the clutch and brake assemblies. During the operation of these dry clutch and brake assemblies, a significant amount of heat was generated. This generation of heat combined with the excessive wear of the friction plates can cause a fading of the brake or clutch system. Other problems associated with the earlier designs of two speed drives included the rigid mounting of the planetary gear system and the problem of poor lubrication of the various components within the drive. Experience has shown that the elements of a large, high-powered planetary gear set are adversely affected if any one of these elements are rigidly mounted. The rigid mounting of one of the elements can lead to an unequal sharing of the load between the mating elements. This unequal sharing of the load in combination with the stopping, starting and reversing of the planetary system leads to increased wear and downtime. The inadequate lubrication of the various components of the drive serves to again increase the wear and down time of the drive system.
Oil shear brakes and clutches have been developed to overcome the problems associated with the earlier designs of two speed drives. In an oil shear clutch or brake system, over 90% of the start/stop inertia is absorbed by a thin, but positive oil film between the friction plates. This thin oil film thus results in little or no wear between the plates and also little or no fading of the braking systems. The thin oil film between the plates also operates to remove the heat generated during the start/stop cycles of the press. With the generated heat being removed from the friction pates, there is no longer a practical limit on the drive trip rate or speed. The oil shear clutch and brake system also eliminates the problems associated with lubrication of the various components of the drive as the drive housing is now filled with lubricating oil for the oil shear clutch and brake system. These oil shear brakes and clutches have also been combined with full floating planetary gear elements to eliminate the unequal sharing of the load between the mating elements.
The two speed drive units incorporating oil shear brakes and clutches as well as full floating planetary gear elements have enjoyed wide acceptance in the two speed drive market. The continued development of these two speed drives is directed towards providing a more compact and lower cost drive without sacrificing the performance characteristics of the drive unit.